Optical disk device for data defect detection and use

ABSTRACT

A disk physical strain correction signal generator outputs a signal obtained by allowing a phase compensation signal to pass a LPF as a disk physical strain correction signal during a normal period. During a defect detection period, it outputs the output signal of the LPF sampled at the time of the defect detection start as the disk physical strain correction signal. A disturbance pulse correction signal is output based upon a disturbance pulse obtained by subtracting the disk physical strain correction signal from the phase compensation signal. The disk physical strain correction signal and the disturbance pulse correction signal are added to output a defect compensation signal. This defect compensation signal is applied as an actuator control signal during the defect detection period. Thus, it is possible to provide an optical disk device which can carry out a stable driving control for a reproducing operation, etc. without losing the continuity of control before and after the defect detection even when the defect detection period is long.

This application is a Continuation of co-pending application Ser. No.09/784,040, filed on Feb. 16, 2001, the entire contents of which arehereby incorporated by reference and for which priority is claimed under35 U.S.C. § 120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disk device such as a DVDand a CD, and more particularly concerns a control system which cancancel adverse effects caused by a defect located on the optical disk.

2. Description of the Background Art

In optical disk apparatuses, various methods for reproducing data from adisk in spite of defects such as scratches and stain (hereinafter,referred to as “defective disks”) located thereon have been proposed,and for example, Japanese Patent Application Laid-Open No. 11-259871(1999) discloses a method in which upon reproducing data from adefective disk, the data is reproduced while interpolating errorsignals.

FIG. 13 is a block diagram that schematically shows a construction(first construction) of a conventional defect compensating device fordefective disks in accordance with the above-mentioned publication.

As illustrated in the Figure, a laser light beam, outputted from alight-emitting optical system 15 including a semiconductor LD (Laserdiode) at the time of data recording or data reproduction, is convergedonto a (DVD) disk 1 through a half mirror 4 and an objective lens 2.Light reflected from the disk 1 at the time of data reproduction is, onthe other hand, inputted to a photoelectric transfer element 5 throughthe half mirror 4.

An actuator driving coil 3 is rigidly connected (firmly connected so asto move integrally) to the objective lens 2, and the driving coil 3 isplaced in a magnetic circuit so that the objective lens 2 is shifted bythe driving coil 3 in a direction perpendicular to the disk 1.

Based upon a photoelectric transfer signal (reflected light information)obtained from the photoelectric transfer element 5, an error detectionmeans 6 outputs an error signal S6 indicating the amount of a controlerror that is a difference between the target tracking position of theobjective lens 2 and the actual position of the objective lens 2 to aselection switch 19 and a disk physical strain correction signalgeneration means 16; thus, the disk physical strain correction signalgeneration means 16 generates a disk physical strain correction signalS16.

Based upon the photoelectric transfer signal obtained from thephotoelectric transfer element 5, a defect detection signal generationmeans 14 generates a detect detection signal SD indicating a detectionstate of the presence or absence of a disk defective area which lacksoptical information due to scratches or stain formed on the surface of adisk 1.

Based upon the defect detection signal SD, the selection switch 19inputs one of the error signal S6 and the disk physical straincorrection signal S16 to a phase compensation means 18. Based upon theinputted signal through the selection switch 19, the phase compensationmeans 18 outputs an actuator control signal S20 (phase compensationsignal S18) to a driver amplifier 10. Based upon the actuator controlsignal S20, the driver amplifier 10 controls the driving coil 3.

This defect compensation device has an arrangement in which the diskphysical strain correction signal generation means 16 for correcting aphysical strain inherent to the disk such as eccentricity and verticaldeviation is added to a generally-used control loop. In other words,functional blocks, numbers 1 to 6 and 10 and 18, have generalcontrol-loop constructions to which functional blocks 14 and 16 forachieving a defective disk reproducing process are added.

Based upon the defect detection signal SD, while detecting a disk error,the selection switch 19 switches the input signal from the phasecompensation means 18 from the error signal S6 to the disk physicalstrain correction signal S16 so that the control loop is cut off. Thedisk physical strain correction signal generation means 16 outputs theaverage value of the error signal S6 in a non-defective area as the diskphysical strain correction signal S16.

An explanation will be given of a generally-used focusing control by thedefect compensation device having the above-mentioned arrangement. Inorder to reproduce information recorded in an information recordinglayer on a disk 1, a laser light beam outputted from the light-emittingoptical system 15 is always converged on the information recording layeron the disk 1 by the objective lens 2. In order to realize this, theobjective lens 2 needs to be position-controlled so as to be alwaysmaintained at a predetermined relative position with respect to the disk1.

The disk 1 has warping, and the absolute amount of the warping isstandardized to, for example, not more than ±300 μm in the DVD standard.Since the disk 1 is rotated, the warping of the disk 1 causes the disk 1to move up and down (hereinafter, referred to as “vertical deviation”);therefore, it is essential to provide tracking control for the objectivelens 2. In this case, the object to be controlled is the objective lens2, the target for the tracking operation is an information recordinglayer of the disk 1, and the kind of control is a relative positionalcontrol between the disk 1 and the objective lens 2. Theposition-controlling process for the objective lens 2 is provided byfeeding a signal formed based upon a relative position error signalbetween the objective lens 2 and the disk 1 back to the driving means ofthe objective lens 2.

The above-mentioned construction is achieved by the following means: ameans for detecting a relative position with respect to the disk 1(constituent sections 1, 2, 4 and 5), a means for generating an error(hereinafter, referred to simply as “FES” (Focus Error Signal) between adetected relative position and a target predetermined relative position(error detection means 6), a phase compensation means for stabilizing aposition control loop (phase compensation mean 18), and a driving meansfor changing the position of the objective lens 2 that is an object tobe controlled (driving coil 3). Here, the phase compensation means 18 isgenerally constituted by a phase-upgrading filter for allowing the phasein the vicinity of 1 KHz to advance. The driving coil 3 is rigidlyconnected to the objective lens 2 so that the objective lens 2 isshifted in a direction perpendicular to the surface of the disk 1 byapplying a driving current to the driving coil 3. An actuator controlsignal (focusing control signal) S20, which is an output of the phasecompensation means 18, controls the driving current of the driving coil3 that is applied by a driver amplifier 10 so that the control systemfor converging the laser light beam onto an information recording layerof the disk 1 is achieved.

The tracking control is only different from the focusing control in thatin addition to the above-mentioned operations, a controlling process forshifting the objective lens 2 in a horizontal direction with respect tothe surface of the disk 1 so as to track a track formed on theinformation recording layer of the disk 1, and is achieved by aconstruction including the above-mentioned focusing control system;therefore, the description thereof is omitted, and in FIG. 13, thecorresponding description is given without distinction between thefocusing and tracking controls. Moreover, the following descriptiongenerally discuss them without the distinction.

Next, an explanation will be given of a defect compensation method bythe conventional defect compensation device shown in FIG. 13. The signalto be applied to the driving coil 3 at the time of detecting a defect isdefined by the actuator control signal S20 obtained by allowing the diskphysical strain correction signal S16 to pass through the phasecompensation means 18. Selection is made between the error signal S6 andthe disk physical strain correction signal S11 by the selection switch19 so that state transitions between a normal controlling state and adefect compensating state is carried out.

The disk physical strain correction signal generation means 61 outputsthe average value of an error signal in a normal state free from adefect as a disk physical strain correction signal S16; therefore, it ispossible to properly maintain the continuity of the error signal S6 evenin the event of a defect, and consequently to realize a defectcompensation.

The essential condition required for a stable, positive defectcompensation process is defined by whether or not a drawing process forthe control loop can be normally performed immediately after the defectcompensation operation, that is, at the time of completion of the defect(hereinafter, referred to as “defect end”). The conditions for stablydrawing the control loop are that the positional difference between thetracking target position at the time of the drawing operation and theposition of the objective lens 2 is set in the vicinity of zero and thatthe relative velocity between the objective lens 2 and the trackingtarget is close to zero. In other words, if the following conditions 1and 2 are satisfied; then it is possible to achieve a stable, positivedefect compensation process.

-   Condition 1: The control error (difference between the position of    the objective lens 2 and the tracking target position) is zero at    the defect end.-   Condition 2: The relative velocity (hereinafter, referred to as    “relative velocity after the defect compensation process”) between    the objective lens 2 and the disk 1 is zero at the defect end.

FIGS. 14A and 14B are explanatory drawings that show defect compensationoperation by the defect compensation device. Referring to FIGS. 14A and14B, the following description will discuss problems with theconventional defect compensation operation. From top to bottom in theFigures, time-wise fluctuations of an all addition signal of thephotoelectric transfer signal (hereinafter, referred to as “RF signal”)obtained from respective areas of the photoelectric transfer element 5,the defect detection signal SD, the error signal S6 and the actuatorcontrol signal S20 are shown, and FIG. 14A shows a case in which nodefect process is carried out, and FIG. 14B shows a case in which theconventional defect process (first method) by using the construction ofFIG. 13 is applied thereto. Here, in FIG. 14B, a normal reproducingprocess is carried out while the defect detection signal SD goes “low”(normal period), and a defect process is carried out while it goes“high” (defect detecting period).

As illustrated in FIG. 14A, in the case of no defect process, from thestart of a defect (a point of time from which the RF signal starts todecrease: hereinafter, referred to simply as “defect start”), adisturbance error is mixed into the error signal S6 as the RF signaldecreases, and at the time when the RF signal becomes zero (that is, thequantity of reflected light from the disk 1 becomes virtually zero), theerror signal S6 itself becomes undetectable (meaningless). Since thecontrol system performs the controlling operation based upon the errorsignal S6, it tracks the disturbance error. At the defect end, since thecontrol system is taken too far by the disturbance error, a greatcontrol error tends to occur, and in the worst case, it sometimesexceeds the detection range (preliminarily determined) of the controlerror, resulting in an inoperable state in the control.

As illustrated in FIG. 14B, in the case of a conventional defectcompensation, when the defect detection signal goes “high”, the diskphysical strain correction signal S16 (a representative value (averagevalue) of the error signal S6 at the time of normal playback) is used inplace of the error signal S6 so as to make an interpolation process, itis possible to reduce the effects of the disturbance error; however, thefollowing problems tends to arise.

In the case of the general defect detection method, in order to ensurestability in the normal reproducing mode, setting is made so as todetect the presence of a defect when the quantity of reflected lightfrom the disk becomes not more than a predetermined value that isslightly lower than the normal peak value, that is, a predeterminednon-sensitive band is provided. With respect to the construction of sucha typical defect detection signal generation means 14, as illustrated inFIGS. 14A and 14B, a construction has been proposed in which, at thetime t1 when a signal obtained by peak-detecting the RF signal becomesnot less than a value V1 that is lower than the normal peak value by ΔV,the defect detection signal SD is allowed to go “high”, thereby enteringthe defect detecting state.

In this construction, during the time ΔT from the defect start until theRF signal has becomes lower than the value V1, the defect detectingprocess becomes inoperable; therefore, there might be an inevitable timelag in the defect detection with respect to a true defect. Even duringthe inevitable time lag period ΔT, since the signal is optically beinginfluenced by the defect, a disturbance error tends to be mixed into theerror signal S6.

In the conventional defect compensation method (first method) shown inFIG. 14B, it is not possible to carry out an interpolation process onthe disturbance error during the inevitable time lag period ΔT. Ingeneral, the residual disturbance error during the time lag period ΔThas frequency components of several hundreds to several kHz, and this isfurther emphasized by the phase compensation means 18 at the time t2when the selection switch 19 makes a switch from the disk physicalstrain correction signal S16 to the error signal S6 upon receipt of thetrailing edge “L” of the defect detection signal SD, with the resultthat the actuator control signal S20 is taken too far, causing aninevitable control deviation at the defect end.

In other words, the conventional defect compensation device shown inFIG. 13 fails to satisfy both of the aforementioned conditions 1 and 2required for a stable, positive defect compensation process.

In order to reduce the influence of the emphasis given on thedisturbance error contained in the error signal S6 by the phasecompensation means 18, for example, an arrangement has proposed in whichthe disk physical strain correction signal generation means 16 and theselection switch 19 are placed on stages after the phase compensationmeans 18.

FIG. 15 is a block diagram that shows a second construction of theconventional defect compensation device. As illustrated in this Figure,the phase compensation means 18 receives the error signal S6, the diskphysical strain correction signal generation means 16 outputs the diskphysical strain correction signal S16 based upon the phase compensationsignal S18, and the selection switch 19 sends either of the phasecompensation signal S18 and the disk physical strain correction signalS16 to the driver amplifier 10 as the actuator control signal S20. Here,since the other arrangements are the same as those shown in FIG. 13, thedescription thereof is omitted.

FIGS. 16A and 16B are explanatory drawings that show a defectcompensation operation by the defect compensation device shown in FIG.15. In these Figures, the definitions on the respective waveforms arethe same as those of FIGS. 14A and 14B, and FIG. 16A shows a case inwhich no defect process is carried out, and FIG. 16B shows a case inwhich the conventional defect process (the second method) is carried outby the construction shown in FIG. 15.

A pulse (hereinafter, referred to as “disturbance pulse”), which iscaused by a disturbance error in the actuator control signal S20, andshown on lower right of FIG. 16B, is improved as compared with the firstmethod, since the actuator control signal S20 is switched to the diskphysical strain correction signal S16 by the selection switch 19 duringthe defect detection period while the defect detection signal SD isgoing “high”; however, the actuator control signal S20 is alwayssubjected to a certain amount of a residual disturbance pulse occurringduring the time lag period ΔT before the time t1. The actuator controlsignal S20 is kicked by the residual disturbance pulse, with the resultthat a control deviation occurs from a predetermined velocity at thedefect end. Consequently, even in the construction shown in FIG. 15, itis not possible to satisfy both of the conditions 1 and 2 required for astable, positive defect compensation operation.

FIGS. 17A to 17C are explanatory drawings that show influences caused bythe application of the disturbance pulse on the velocity and position ofthe actuator. Referring to FIGS. 17A to 17C, the following descriptionwill generally discuss the above-mentioned problems. Supposing that themechanical characteristics of the actuator including the driving coil 3that is a subject to be controlled are secondary systems, the position,velocity and acceleration (in proportion to the signal applied to thedriving coil 3) of the objective lens 2 are defined as shown byExpressions (I) to (III).Position=X(t)  (I) [Expression 1]Velocity={dot over (X)}(t)  (II) [Expression 2]Acceleration={umlaut over (X)}(t)  (III) [Expression 3]

In FIGS. 17A to 17C, FIG. 17A represents the acceleration, FIG. 17Brepresents the velocity, and FIG. 17C represents the positional changewith time. Assuming that the disturbance pulse has a rectangularwaveform as shown in FIG. 17A, the influences this rectangular waveformexerts on the velocity and position of the actuator are explained asfollows:

(1) During the application of the disturbance pulse, the velocity of theactuator increases in a manner of a linear function, and when theapplication of the disturbance pulse is stopped, the velocity at thetime of the end of the disturbance pulse is maintained (see FIG. 17B).

(2) During the application of the disturbance pulse, the position of theactuator increases in a manner of a quadratic function, and even whenthe application of the disturbance pulse is stopped, the position keepsincreasing linearly while maintaining the gradient at the time of theend of the disturbance pulse (see FIG. 17C).

The above-mentioned facts indicate that due to (1), it is not possibleto satisfy the condition 2 required for a stable, positive defectcompensation operation (that is, the relative velocity after the defectcompensation process is zero), and that due to (2), it is not possibleto satisfy the condition 1 (that is, the control error is zero). Sincethe timing of the disturbance pulse end coincides with the start of thedefect detection period, the conventional defect compensation methodmakes the positional error greater in proportion to the defect detectionperiod, sometimes resulting in a case in which the error detection rangeis exceeded.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, an optical diskdevice comprises a light emitting means for emitting light to an opticaldisk, a driving means for carrying out a predetermined operation withrespect to the optical disk based upon a driving control signal, areflected light information detection means for detecting reflectedlight information related to reflected light from the optical disk, anormal control signal generation means for generating a normal controlsignal for determining the amount of control in the predeterminedoperation based upon the reflected light information, and a defectdetection signal generation means for generating a defect detectionsignal for specifying the presence or absence of a defect area lackingoptical information in the optical disk based upon the reflected lightinformation. In this arrangement, it is defined that a period in whichthe defect detection signal indicates that there is no defect area isdefined as a normal period and a period in which the defect detectionsignal indicates that there is a defect area is defined as a defectdetection period, and this arrangement is further provided with: a lowfrequency correction signal generation means for performing a filteringprocess to the normal control signal, the filtering process allowing avarying frequency of the normal control signal to pass and removing ahigh frequency component of the same to generate a low frequencycomponent signal as a low frequency correction signal in the normalperiod, and for generating the low frequency component signal sampled atthe time of defect detection start when the normal period is switched tothe defect detection period as the low frequency compensation signal inthe defect detection period; a disturbance pulse correction signalgeneration means for recognizing a disturbance pulse based upon adifference between the low frequency correction signal and the normalcontrol signal during a period from the time of the defect detectionstart back to a predetermined point of time to generate a disturbancepulse correction signal containing a first correction pulse obtained byinverting a polarity of the disturbance pulse with the same impulse withthe disturbance pulse; an addition means for obtaining a defectcompensation signal by adding the disturbance pulse correction signal tothe low frequency correction signal; and a signal selection means forselecting the normal control signal as the driving control signal duringthe normal period, and selecting the defect compensation signal as thedriving control signal during the defect detection period.

Moreover, in a second aspect of the present invention which relates toan optical disk device according to the first aspect, the disturbancepulse correction signal includes a second and third correction pulsesucceeding to the first correction pulse, the second correction pulseincludes a pulse obtained by inverting the polarity of the disturbancepulse with the same impulse as the disturbance pulse, the thirdcorrection pulse includes a pulse that has the same polarity and thesame impulse as the disturbance pulse.

Moreover, in a third aspect of the present invention which relates tothe optical disk device according the first or second aspect, thepredetermined operation includes a reproducing operation of informationrecorded on the optical disk, and the predetermined time is set basedupon a reproducing linear velocity that is a linear velocity at the timeof the reproducing operation of the optical disk.

Moreover, in a fourth aspect of the present invention which relates tothe optical disk device according to the first to third aspects, thedisturbance pulse correction signal generation means comprises apredetermined number of registers that successively stores thedisturbance pulses while shifting them in a predetermined order duringthe normal period, the predetermined time includes a period of timeduring which the registers carried out the storing process, the opticaldisk device further comprising a correction pulse generation controlmeans for generating the disturbance pulse correction signal based uponthe disturbance pulses being reproduced by reading out the data storedin the registers at the time of defect detection start in thepredetermined order, during the defect detection period.

In the optical disk device according to the first aspect, during thedefect detection period, a defect compensation signal, which is formedby adding the disturbance pulse correction signal to the low frequencycorrection signal, is used as a driving control signal for the drivingmeans.

A low-frequency correction signal is a signal formed by sampling alow-frequency component signal that is formed by removing a disturbancepulse that is a high-frequency component from a normal control signaland allowing fluctuation frequency components of the normal controlsignal to pass; therefore, its defect detection period is generallysmall as compared with the fluctuation period of the normal controlsignal so that it is possible to maintain the controlling continuity ofthe driving means at the time when the driving control signal isswitched from the defect compensation signal to the normal controlsignal upon returning from the defect detection period to the normalperiod.

Moreover, the disturbance pulse correction signal contains the firstcorrection pulse obtained by inverting the polarity with the sameimpulse as disturbance pulses generated during a period from the time ofthe defect detection start back to a predetermined point of time;therefore, it becomes possible to virtually cancel completely adverseeffects given by a disturbance pulse (mixed to the normal control signalduring a time period immediately before the defect detection) to thecontrol velocity of the driving means, independent of the length of thedefect detection period. Therefore, it is possible to control thedriving means in a stable manner even when the defect detection periodis long.

In the optical disk device according to the second aspect, thedisturbance pulse correction signal contains the first to thirdcorrection pulses so that it becomes possible to virtually cancelcompletely adverse effects given by a disturbance pulse to the controlposition of the driving means by using the second and third correctionpulses. Therefore, it is possible to control the driving means morestably even when the defect detection period is long.

In the optical disk device according to the third aspect, thepredetermined time that is a recognition period of a disturbance pulseis set based upon the reproducing linear velocity of the optical disk sothat it is set to a period of time suitable for the pulse generationtime of the disturbance pulse that is positively correlated with thereproducing linear velocity.

In the optical disk device according to the fourth aspect, during thenormal period, disturbance pulses are stored in a predetermined numberof registers serving as shift registers, and during the defect detectionperiod, the data stored in the registers at the defect detection startpoint is read out in a predetermined order so that the disturbancepulses are reproduced accurately. Therefore, the disturbance pulsecorrection signal generation means is allowed to generate a disturbancepulse correction signal which can correct adverse effects caused by thedisturbance pulses with high precision. Moreover, the predetermined timethat is a recognition time for a disturbance pulse can be set bychanging the number of registers.

An object of the present invention is to obtain an optical disk devicewhich can maintain the continuity of the control even before and after adefect detection without losing it, and provide a stable driving controloperation for reproduction, etc. even when the defect detection periodis long (in other words, the defect area is large, or the reproducingvelocity is slow).

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are explanatory drawings that show the best-suitedsolution of a disk physical strain correction signal;

FIGS. 2A to 2C are explanatory drawings that show the effect ofapplication of a disturbance pulse correction signal to a disturbancepulse;

FIGS. 3A to 3C are explanatory drawings that show the effect ofapplication of a plurality of disturbance pulse correction signals to adisturbance pulse;

FIG. 4 is a block diagram that shows the construction of a disk devicein accordance with a first preferred embodiment of the presentinvention;

FIG. 5 is a block diagram that shows the inner construction of aphysical strain correction signal generation means in FIG. 4;

FIG. 6 is a block diagram that shows an example of the innerconstruction of a disturbance pulse correction signal generation meansin FIG. 4;

FIGS. 7A and 7B are explanatory drawings that show a specific structuralexample of a disturbance pulse memory means in FIG. 6;

FIGS. 8A to 8D are explanatory drawings that show a detection method ofa disturbance pulse;

FIGS. 9A and 9B are explanatory drawings that show the results of thedefect compensation operation of the optical disk device in accordancewith the first preferred embodiment of the present invention;

FIG. 10 is a flow chart that shows a control operation by a memoryoutput control means of a second preferred embodiment;

FIGS. 11A and 11B are explanatory drawings that show the results of thedefect compensation operation of the optical disk device in accordancewith the second preferred embodiment of the present invention;

FIGS. 12A and 12B are explanatory drawings that show an example of theapplication of a disturbance pulse memory means in accordance with athird preferred embodiment of the present invention;

FIG. 13 is a block diagram that schematically shows a conventionaldefect compensation device (first construction);

FIGS. 14A and 14B are explanatory drawings that show a defectcompensation operation by the defect compensation device of FIG. 13;

FIG. 15 is a block diagram that schematically shows a conventionaldefect compensation device (second construction);

FIGS. 16A and 16B are explanatory drawings that show a defectcompensation operation by the defect compensation device of FIG. 15; and

FIGS. 17A to 17C are explanatory drawings that show effects of theapplication of a disturbance pulse exerted on the speed and position ofthe actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

<Principle of the Invention>

At a defect portion on an optical disk, an error signal forms a falseerror signal that is a disturbance error signal. For this reason, in thedefect compensation control, upon detection of a defect, the controlloop needs to be completely cut off, and upon completion of the defect,the control needs to be led in immediately, while maintaining thecontinuity of the control. The detection of a defect means that there isa lack of error signal; therefore, it is understood that, in order toensure a stable, continuous lead-in operation at the defect end, a diskphysical strain correction signal is required instead of the errorsignal, so as to provide a tracking operation on the disk physicalstrain (eccentricity and vertical deviation) even during defect period.

Therefore, the control signal that is applied to the driving coil 3 atthe time of the error detection is defined as the addition of the diskphysical strain correction signal used for tracking and interpolatingoperations with respect to the disk physical strain during the defectdetection period and the disturbance pulse correction signal forcorrecting the influences of the disturbance pulse that have beendiscussed in the Prior Art section. The following description willdiscuss the disk physical strain correction signal and the disturbancepulse correction signal.

(Optimal Disk Physical Strain Correction Signal)

FIGS. 1A to 1C are explanatory drawings that show the best suitedsolution for the disk physical strain correction signal. The opticaldisk, which is a tracking target, has eccentricity and verticaldeviation as described earlier; therefore, since the disk is rotated,the tracking target forms a frequency function.

FIG. 1A shows the disk physical strain (eccentricity and verticaldeviation) that is the tracking target, FIG. 1B shows a phasecompensation signal which forms a basis of the actuator control signalat the time of the control operation, and is generated based upon theerror signal, and FIG. 1C shows an output signal obtained by allowingthe phase compensation signal to pass through a low-pass filter. In theFigures, the tracking target forms a periodic function with one rotationcycle T of the disk, and since the phase compensation signal tracksthis, it has a periodic function synchronizing to the tracking target.Here, time t11 and time t12 show defect detection times on a disk 1.

As described earlier, the phase compensation signal is obtained byemphasizing an error signal in the range of several hundreds Hz toseveral KHz using the phase compensation means, and therefore has awaveform containing noise. Thus, it is not possible to use the phasecompensation signal as an actuator control signal, as it is, or evenwhen it is sample-held. For this reason, a filter, which transmits basicfrequency components (fluctuation frequency components of the phasecompensation signal), and regulates noise components in high bands, thatis, a low-pass filter whose cut-off frequencies are set higher than thedisk rotation frequency, is used so as to extract only the frequencycomponents of the disk physical strain that are the tracking target fromthe phase compensation signal, and this is utilized as the disk physicalstrain correction signal (low-frequency correction signal).

With this method, even when a defect portion is located at an arbitraryposition in one rotation cycle of the disk, the phase compensationsignal is interpolated by the output of the low-pass filter; thus, it ispossible to obtain an optimal signal from the macroscopic point of view.

(Disturbance Pulse Correction Signal)

Referring to FIGS. 17A to 17C, influences caused by disturbance pulseshave been explained. Here, the following description will discuss how tonullify the influences of disturbance pulses.

(1) Means for Satisfying Condition 2 Required for Obtaining Stable,Positive Defect Compensation (the Relative Velocity After DefectCompensation is Zero)

Since the control target is in the secondary system, the application ofa pulse having the reversed polarity with the same impulse as theimpulse (the result obtained by multiplying acceleration by time) of adisturbance pulse makes the impulse exerted on the control target zero,thereby making the velocity zero. Therefore, the disturbance pulsecorrection signal is determined so as to have the same absolute value asthe impulse of the disturbance pulse and the reversed polarity thereto.

FIGS. 2A to 2C are explanatory drawings that show the effects ofapplication of the disturbance pulse correction signal to a disturbancepulse. As illustrated in FIG. 2A, the correction pulse SC1 is appliedimmediately after the disturbance pulse OP, that is, immediately afterthe detection of a defect. This is because if there is a delay in thetiming of the application of the correction pulse SC1, the positionalerror increases at the defect end in proportion to the correspondingdelay time. In this manner, the application timing of the correctionpulse SC1 is set so as to take place immediately after the disturbancepulse OP so that the positional error at the defect end can beminimized. In the cases of FIGS. 2A to 2C, the waveform of thecorrection pulse SC1 is set so as to have the same waveform as thedisturbance pulse with the reversed polarity thereto; however, asdescribed earlier, it is clear that if the impulse is the same, the sameeffects can be obtained.

The application of the correction pulse SC1 as described above makes thevelocity of the correction pulse SC1 become zero upon completion of itsapplication. Therefore, after the application of the correction pulseSC1, the positional error ΔP at the defect end is set to a predeterminedvalue without depending on the size of the defect or the length of thedefect detection time. If this predetermined value is located within arange that allows the control system to carry out a stable lead-inoperation, it is possible to realize a stable defect compensation byusing only the present method.

(2) Means for Satisfying Condition 1 Required for Obtaining Stable,Positive Defect Compensation (the Control Error is Zero)

In addition to means for satisfying condition 2 required for obtainingstable positive defect compensation, the following description alsodiscuss the means for satisfying condition 1. It has already beendescribed that, although the application of means (1) ensures that thevelocity becomes zero, the positional error ΔP having a predeterminedvalue arises. Since the positional error ΔP is exerted as a result ofthe continuous applications of the disturbance pulse OP and thecorrection pulse SC1, the positional error ΔP can be reduced to zero bysuccessively applying signals respectively having reversed polarities ofthe disturbance pulse OP and the correction pulse SC1 in succession tothe disturbance pulse OP and the correction pulse SC1.

FIGS. 3A to 3C are explanatory drawings that show effects of a case inwhich a plurality of disturbance pulse correction signals are applied.As illustrated in the Figures, in succession to the correction pulse SC1shown in FIGS. 2A to 2C, a correction pulse SC2 and a correction pulseSC3 are further applied. The correction pulse SC2, which has the samepolarity and the same waveform as the correction pulse SC1 (that is, thesame waveform as the disturbance pulse OP and the reversed polaritythereto), is applied immediately after the correction pulse SC1. Theapplication of the correction pulse SC2 allows the velocity of thecontrol object indicated by (b) to have the same absolute value as thevelocity raised by the application of the disturbance pulse OP with thereversed polarity thereto.

As indicated by (c), the position of the control target is being shiftedin a direction so as to correct the positional error. The correctionpulse SC3, which has a waveform having the same absolute value as thecorrection pulse SC1 with the reversed polarity thereto (that is, thesame polarity and the same waveform as the disturbance pulse OP), isapplied immediately after the correction pulse SC2. The application ofthe correction pulse SC3 makes the velocity of the control target becomezero (see FIG. 3B), and at this time, as indicated by (c), with respectto the position of the control target, it becomes possible to correctthe positional error ΔP to virtually zero. Therefore, in principle, theapplication of the present means (2) makes it possible to eliminate thepositional error even when the defect is large, and also to set therelative speed to the disk to zero. Since these means satisfy both ofthe conditions (1) and (2) required for obtaining stable, positivedefect compensation, independent on the size of a defect in the disk 1,it is possible to realize a stable, positive defect compensation.

Based upon the above-mentioned analytic explanation, the followingdescription will discuss one preferred embodiment of the present defectcompensation system of the present invention.

<First Preferred Embodiment>

FIG. 4 is a block diagram that shows a construction of a disk device inaccordance with the first preferred embodiment of the present invention.As illustrated in this Figure, a control loop switch 7, which receivesan error signal S6 and a fixed electric potential signal S0 from anerror detection means 6, supplies the fixed electric potential signal S0to a phase compensation means 8 during the defect detection periodindicating a defect detection state with the defect detection signal SDgoing “high”, while it supplies the error signal S6 to the phasecompensation means 8 during the normal period indicating a normal statewith the defect detection signal SD going “low”.

Based upon the signal obtained through a control loop switch 7, thephase compensation means 8 generates a phase compensation signal S8.

Upon receipt of the phase compensation signal S8 and the defectdetection signal SD, the disk physical strain correction signalgeneration means 11 generates a disk physical strain correction signalS11 based upon the phase compensation signal S8 in accordance with thetiming control of the defect detection signal SD.

A disturbance pulse compensation signal generation means 13, whichreceives the phase compensation signal S8, the disk physical straincorrection signal S11 and the defect detection signal SD, generates adisturbance pulse compensation signal S13 based upon the timing controlof the defect detection signal SD, the phase compensation signal S8 andthe disk physical strain correction signal S11.

An addition means 12 outputs a defect compensation signal S12 by addingthe disk physical strain correction signal S11 and the disturbance pulsecorrection signal S13.

A selection switch 9, which receives the phase compensation signal S8and the defect compensation signal S12, supplies the defect compensationsignal S12 to the driver amplifier 10 as an actuator control signal S20during the defect detection period with the defect detection signal SDgoing “high”, while it supplies the phase compensation signal S8 as theactuator control signal S20 during the normal period with the defectdetection signal SD going “low”. In other words, the phase compensationsignal S8 forms the normal actuator control signal S20, and the defectcompensation signal S12 forms the actuator control signal S20 at thetime of defect detection. Here, the other arrangements are the same asthose of FIG. 15; therefore, the description thereof is omitted.

A control loop switch 7 turns off during the defect period with thedefect detection signal SD going “high” (fixed to the fixed electricpotential signal S0) so that a non-linear control error in the defect isblocked from the disk physical strain correction signal generation means11.

As described earlier, the defect compensation signal S12, outputted fromthe addition means 12, is defined by the sum of the physical straincorrection signal S11 that is an output of the disk physical straincorrection signal generation means 11 and the disturbance pulsecorrection signal S13 that is the output of the disturbance pulsecorrection signal generation means 13.

The disk physical strain correction signal generation means 11 has afunction for supplying a signal to the driving coil 3 so as not to allowthe position of the control target (an objective lens 2) to track ordeviate from the eccentricity or vertical deviation during the defectperiod.

FIG. 5 is a block diagram that shows the inner construction of the diskphysical strain correction signal generation means 11. As illustrated inthis Figure, the disk physical strain correction signal generation means11 is constituted by a LPF (low-pass filter) 11 a and a sample holdmeans 11 b. The LPF11 a sets a cut-off frequency to a frequency higherthan the disk rotation frequency, and waveform-shapes the phasecompensation signal S8 shown in FIG. 1B into a signal shown in FIG. 1C.

The sample hold means 11 b holds the output signal of the low-passfilter 11 a at the time of the rising edge to “high” (detect detectionstart time) of the defect detection signal SD. The output from thesample hold 11 b forms the disk physical strain correction signal S11,and this is supplied to the addition means 12 and the disturbance pulsecorrection signal generation means 13.

FIG. 6 is a block diagram that shows one example of the innerconstruction of the disturbance pulse correction signal generation means13. As illustrated in this Figure, the disturbance pulse correctionsignal generation means 13 is constituted by a disturbance pulsedetection means 13 a, a disturbance pulse memory means 13 b and a memoryoutput control means 13 c.

The disturbance pulse detection means 13 a subtracts the disk physicalstrain correction signal S11 from the phase compensation signal S8 so asto detect a disturbance pulse S13 a. Based upon “L”/“H” of the defectdetection signal SD, the disturbance pulse memory means 13 b carries outa writing/reading operation. At the time of writing operation, it storesdisturbance pulses S13 a detected by the disturbance pulse detectionmeans 13 a from the latest one back to those detected during apredetermined time, in synchronism with the disturbance pulse samplingsetting signal S21, and at the time of reading out operation, reads outthe stored pulses under the control of the memory output control means13 c.

The memory output control means 13 c receives the defect detectionsignal SD, and during the defect detection period with the defectdetection signal SD going “high”, controls the contents of the outputand the output sequence of the disturbance pulse correction signal basedupon the disturbance pulses stored in the disturbance pulse memory means13 b, and inverts the polarity of data read out from the disturbancepulse memory means 13 b, and outputs the resulting signal as adisturbance pulse correction signal S13.

FIGS. 7A and 7B are explanatory drawings that show a specific structuralexample of the disturbance pulse memory means 13 b. FIG. 7A shows thewriting operation with the defect detection signal SD going “low”, andFIG. 7B shows the reading-out operation with the defect detection signalSD going “high”.

The disturbance pulse memory means 13 b is constituted by n number ofregisters R0 to R(n−1) each having a predetermined bits. At the timewhen the defect detection signal SD goes “low” (normal mode), the nnumber of registers R0 to R(n−1) function as shift registers that shiftin the order of 0 to (n−1) so that they shift from register R0 to R(n−1)while successively inputting the disturbance pulses S13 a starting withthe register R0 in synchronism with the disturbance pulse samplingsetting signal S21.

At the time when the disturbance detection signal goes “high” (defectdetection mode), the writing operation of the disturbance pulse isstopped, and the sequence shifts to the reading-out operation whilemaintaining the stored disturbance pulses. In the reading-out operation,in synchronism with the disturbance pulse sampling setting signals S21,data stored in the registers R0 to R(n−1) is inverted in its polarity,and successively outputted.

FIGS. 8A to 8D are explanatory drawings that show the detecting methodof the disturbance pulses. FIGS. 8A to 8D are drawings that show thetime axis in the vicinity of defect detection time t11 of FIGS. 1A to 1Cin an enlarged manner.

FIG. 8A shows a defect detection signal SD, FIG. 8B shows a phasecompensation signal S8, FIG. 8C shows a disk physical strain correctionsignal S11, and FIG. 8D shows a disturbance pulse S13 a, respectively.Here, for convenience of explanation, waveforms are obtained in a casein which the control loop switch 7 is inputting the error signal S6independent of the defect detection signal SD.

As shown in the Figures, by subtracting the component of the diskphysical strain correction signal S11 (a low-frequency component signalobtained by removing a high-frequency component including a disturbancepulse from the phase compensation means 8) from an abnormal rise of thephase compensation signal S8 in the vicinity of time t11 that is thedefect start, it is possible to extract the disturbance pulse S13 aaccurately.

FIG. 9A and FIG. 9B are explanatory drawings that show the results ofthe defect compensation operation by the optical disk device inaccordance with the first preferred embodiment of the present invention.FIG. 9A and FIG. 9B show the operation of a defect compensation in thepresent invention carried out under the same conditions as those shownin FIGS. 14A and 14B that have been explained in the Prior Art Section.The definitions of the respective waveforms are the same as those shownin FIGS. 14A and 14B; and FIG. 9A shows a case in which no defectprocess is carried out as in the cases of FIG. 14A and FIG. 16A, andFIG. 9B shows a case in which a defect process is carried out by theoptical disk device of the first preferred embodiment.

The actuator control signal S20 of FIG. 9B shows that the compensationpulse SC1 is outputted immediately after defect detection time t1, andthat this signal allows the velocity of the objective lens 2 to becomezero, with the result that the error signal S6 is made smaller at thedefect end. For this reason, the control lead-in operation can becompleted immediately in a stable manner, and the amplitude degradationof the RF signal at the defect end becomes smaller, thereby making itpossible to ensure a stable, positive defect compensation operation.

<Second Preferred Embodiment>

The second preferred embodiment relates to an optical disk device whichcan realize a defect compensation operation with higher precision. Asalready explained by reference to FIG. 3A to 3C, in the arrangement ofthe second preferred embodiment, the means (2) satisfying both theconditions (1) and (2) required for a stable, positive defectcompensation is adopted, and with respect to the disturbance pulsecorrection signal, not only the correction pulse SC1, but also thecorrection pulses SC2 and SC3 are successively applied. Theabove-mentioned arrangement is realized by modifying the contents of thecontrol of the memory output control means 13 c in the first preferredembodiment in the following manner so as to satisfy the means (2).

In the same manner as the first preferred embodiment, the disturbancepulse memory means 13 b of the second preferred embodiment is alsoconstituted by n number of registers R0 to R(n−1), each having apredetermined bits. At the time when the defect detection signal SD goes“high” (normal mode), the n number of registers R0 to R(n−1) function asshift registers in the same manner as the first preferred embodiment,and successively input the disturbance pulses S13 a starting with theregister R0 in synchronism with the disturbance pulse sampling settingsignal S21.

At the time when the disturbance detection signal goes “high” (defectdetection mode), the disturbance pulse memory means 13 b stops thewriting operation of the disturbance pulse, and the sequence shifts tothe reading-out operation while maintaining the stored disturbancepulses S13 a.

FIG. 10 is a flow chart that shows the contents of the reading-outoperation from the disturbance pulse storage means 13 b carried outunder the control of the memory output control means 13 c at the timewhen the defect detection signal SD goes “low”.

As shown in the Figure, at step S1, in synchronism with the disturbancepulse sampling setting signal S21, data stored in the registers R0 toR(n−1) is inverted in its polarity, and successively outputted, therebyforming a correction pulse SC1.

Thereafter, at step S2, in the same manner as step S1, in synchronismwith the disturbance pulse sampling setting signal S21, data stored inthe registers R0 to R(n−1) is inverted in its polarity, and successivelyoutputted, thereby forming a correction pulse SC2.

Moreover, at step S3, in synchronism with the disturbance pulse samplingsetting signal S21, data stored in the registers R0 to R(n−1) issuccessively outputted with its polarity maintained as it is, therebyforming a correction pulse SC3.

In this manner, the disk device of the second preferred embodiment isrealized by modifying the contents of the control of the memory outputcontrol means 13 c from the first preferred embodiment to thearrangement shown in FIG. 10 so as to satisfy the means (2). Therefore,the other arrangements are the same as those of the disk device of thefirst preferred embodiment shown in FIG. 4.

FIG. 11A and FIG. 11B are explanatory drawings that show the results ofthe defect compensation operation by the optical disk device inaccordance with the second preferred embodiment of the presentinvention. FIG. 11A and FIG. 11B show the operation of a defectcompensation in the present invention carried out under the sameconditions as those shown in FIGS. 14A and 14B that have been explainedin the Prior Art Section. The definitions of the respective waveformsare the same as those shown in FIGS. 14A and 14B; and FIG. 11A shows acase in which no defect process is carried out as in the cases of FIG.9A, and FIG. 11B shows a case in which a defect process is carried outby the optical disk device of the second preferred embodiment.

The actuator control signal S20 of FIG. 11B shows that the compensationpulse SC1, the compensation pulse SC2 and the compensation pulse SC3 areoutputted immediately after defect detection time t1, and that thesesignals allow the velocity of the objective lens 2 to become zero, andalso allow the control deviation at the defect end to become zero. Forthis reason, the control lead-in operation can be completed immediatelyin a stable manner, and the amplitude degradation of the RF signal atthe defect end becomes smaller, thereby making it possible to ensure astable, positive defect compensation operation regardless of the degreeof defects on the disk 1.

<Third Preferred Embodiment>

It has already been described that the disturbance pulse is caused by adisturbance error mixed into the error signal S6 at the defect start.Therefore, the time length of the disturbance pulse forms a functiondependant on the reproducing linear velocity (linear velocity of thedisk 1 at the time of reproduction), and it is clear that as the linearvelocity becomes faster, the time length of the disturbance pulsebecomes shorter and as the linear velocity becomes slower, the timelength of the disturbance pulse becomes longer. Consequently, it ispreferable to vary the disturbance pulse memory time in response to thelinear velocity. In other words, the third preferred embodiment realizesan optical disk device that can store disturbance pulses accurately.

The optical disk device of the third preferred embodiment has the samestructure as that of the first and second preferred embodiments, exceptthat only the construction of the disturbance pulse correction signalgeneration means 13 is slightly different. The disturbance pulse memorymeans 13 b is constituted by m number of registers R0 to R(m−1), eachhaving predetermined bits, and the m number of registers are set so asto respond to the slowest linear velocity.

Then, among the m number of registers 0 k to R(m−1) prepared based uponthe reproducing linear velocity, the number of actually-used registers kis set. In other words, when the reproducing linear velocity is slow,the number of registers k is set greater (the maximum m); in contrast,when it is fast, the number of registers k is set smaller. In thismanner, the disturbance pulse memory time (the memory time using the knumber of actually-used registers) is controlled so as to conform to thereproducing linear velocity.

FIGS. 12A and 12B are explanatory drawings that show an example of theapplication of the disturbance pulse memory means 13 b in the thirdpreferred embodiment. FIG. 12A shows a writing operation with the defectdetection signal SD going “low”, and FIG. 12B shows a reading-outoperation with the defect detection signal SD going “high”.

The m number of registers R0 to R(m−1), each having predetermined bits,in the disturbance pulse memory means 13 b are classified into anactually-used register group 13 b 1 consisting of the actually-used k(k=1 to m) number of registers R0 to R(k−1) and an unused register group13 b 2 consisting of the unused (m−k) number of registers Rk to R(m−1).

At the time when the defect detection signal SD is “low”, the writingoperation is carried out while using the registers R0 to R(k−1) of theactually-used register group 13 b 1 as shift registers that shift in theorder of 0 to (k−1), and the registers Rk to R(m−1) of theunused-register group 13 b 2 are completely unused.

In contrast, at the time when the disturbance detection signal is“high”, the actually-used register group 13 b 1 successively output datain the order to R0 to R(k−1), while the registers Rk to R(m−1) of theunused register group 13 b 2 are completely unused. Here, any of thedisturbance pulse correction signals in the first preferred embodimentor the second preferred embodiment can be generated by changing thecontents of the control of the memory output control means 13 c.

Moreover, the cycle of the disturbance pulse sampling setting signal S21serving as a sampling clock and the other constituent algorithms are setin the same manner as the first and second preferred embodiments. Thisarrangement makes it possible to realize a disturbance pulse storingoperation suitable for the disturbance pulse length and a stable defectcompensation.

Here, an explanation has been given of a disturbance pulse storingoperation suitable for the reproducing linear velocity that is carriedout by changing the number k of the actually-used registers withoutchanging the cycle of the disturbance pulse sampling setting signal S21;however the number k of registers may be fixed, and the cycle of thedisturbance pulse sampling setting signal S21 may be changed based uponthe reproducing linear velocity. This arrangement of course makes itpossible to provide the same effects.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous othermodifications and variations can be devised without departing from thescope of the invention.

1. An optical disk device comprising: light emitting means for emittinglight to an optical disk; driving means for carrying out a predeterminedoperation with respect to said optical disk based upon a driving controlsignal; reflected light information detection means for detectingreflected light information related to reflected light from said opticaldisk; normal control signal generation means for generating a normalcontrol signal for determining amount of control in said predeterminedoperation based upon said reflected light information; defect detectionsignal generation means for generating a defect detection signal forspecifying presence or absence of a defect area lacking opticalinformation in said optical disk based upon said reflected lightinformation, a period in which said defect detection signal indicatesthat there is no defect area being defined as a normal period and aperiod in which said defect detection signal indicates that there is adefect area being defined as a defect detection period; low frequencycorrection signal generation means for performing a filtering process tosaid normal control signal, said filtering process allowing a varyingfrequency of said normal control signal to pass and removing a highfrequency component of the same to generate a low frequency componentsignal as a low frequency correction signal in said normal period, andfor generating said low frequency component signal sampled at the timeof defect detection start when said normal period is switched to saiddefect detection period as said low frequency compensation signal insaid defect detection period; disturbance pulse correction signalgeneration means for recognizing a disturbance pulse based upon adifference between said low frequency correction signal and said normalcontrol signal during a period from the time of said defect detectionstart back to a predetermined point of time to generate a disturbancepulse correction signal containing a first correction pulse obtained byinverting a polarity of said disturbance pulse with the same impulsewith said disturbance pulse; addition means for obtaining a defectcompensation signal by adding said disturbance pulse correction signalto said low frequency correction signal; and signal selection means forselecting said normal control signal as said driving control signalduring said normal period, and selecting said defect compensation signalas said driving control signal during said defect detection period. 2.The optical disk device according to claim 1, wherein said predeterminedoperation includes a reproducing operation of information recorded onsaid optical disk, and said predetermined time is set based upon areproducing linear velocity that is a linear velocity at the time of thereproducing operation of said optical disk.
 3. The optical disk deviceaccording to claim 1, wherein said disturbance pulse correction signalgeneration means comprises a predetermined number of registers thatsuccessively stores said disturbance pulses while shifting them in apredetermined order during said normal period, said predetermined timeincludes a period of time during which said registers carries out saidstoring process, said optical disk device further comprising: acorrection pulse generation control means for generating saiddisturbance pulse correction signal based upon said disturbance pulsesbeing reproduced by reading out the data stored in said registers atsaid time of defect detection start in said predetermined order, duringsaid defect detection period.
 4. The optical disk device according toclaim 1, wherein said disturbance pulse correction signal includes asecond and third correction pulse succeeding to said first correctionpulse, said second correction pulse includes a pulse obtained byinverting a polarity of said disturbance pulse with the same impulse assaid disturbance pulse, said third correction pulse includes a pulsethat has the same polarity and the same impulse as said disturbancepulse.
 5. The optical disk device according to claim 4, wherein saiddisturbance pulse correction signal generation means comprises apredetermined number of registers that successively stores saiddisturbance pulses while shifting them in a predetermined order duringsaid normal period, said predetermined time includes a period of timeduring which said registers carries out said storing process, saidoptical disk device further comprising: a correction pulse generationcontrol means for generating said disturbance pulse correction signalbased upon said disturbance pulses being reproduced by reading out thedata stored in said registers at said time of defect detection start insaid predetermined order, during said defect detection period.
 6. Theoptical disk device according to claim 4, wherein said predeterminedoperation includes a reproducing operation of information recorded onsaid optical disk, and said predetermined time is set based upon areproducing linear velocity that is a linear velocity at the time of thereproducing operation of said optical disk.
 7. The optical disk deviceaccording to claim 6, wherein said disturbance pulse correction signalgeneration means comprises a predetermined number of registers thatsuccessively stores said disturbance pulses while shifting them in apredetermined order during said normal period, said predetermined timeincludes a period of time during which said registers carries out saidstoring process, said optical disk device further comprising: acorrection pulse generation control means for generating saiddisturbance pulse correction signal based upon said disturbance pulsesbeing reproduced by reading out the data stored in said registers atsaid time of defect detection start in said predetermined order, duringsaid defect detection period.